The present invention relates to a polishing machine for polishing the surface of a workpiece such as a wafer to be processed and, more particularly, it relates to a polishing machine wherein the workpieces are fitted in carriers, which are placed between upper and lower surface plates, which are rotated relative to each other and the carriers are rotated round a sun gear by means of the sun gear and an internal ring gear, turning round their own axes, whereby the surfaces of the workpieces to be processed are polished by an abrasive cloth or cloths attached to one or both of the surface plates.
FIG. 1 shows a conventional polishing machine of this type. This type of the polishing machine is proposed in Japanese Utility Model Disclosure No. 68747, 1982. The polishing machine includes upper and lower surface plates 10 and 12. Abrasive cloths 14 and 16 are stuck to the upper and lower surface plates. The lower surface plate 12 is rotatably supported by a base 18 through bearings while connected to a driving device (not shown) through a gear 20. On the other hand, the upper surface plate 10 is suspended, movable up and down, from a main cylinder 22 fixed to a frame 24. The upper surface plate 10 has a bore 26 with which a spline shaft 28 of a shaft 30 is detachably engaged. The shaft 30 is connected to a driving device (not shown) through a gear 32.
A plurality of carriers 34 are placed between the upper and lower surface plates 10 and 12, and each of the carriers 34 has a plurality of bores into each of which a workpiece W to be processed is fitted. Each of the carriers 34 is in mesh with both of sun gear 36 and internal ring gear 38. The sun gear 36 and the internal ring gear 38 are arranged concentric with each other. The sun gear 36 is rotated by a gear 42 attached to a hollow driving shaft 40, while the internal ring gear 38 by a gear 44. Therefore, the carriers 34 are rotated round the sun gear 36, turning round their own axes, as the planet gear of planetary gears.
In the case of this conventional polishing machine, however, the internal ring gear 38 or sun gear 36 wears when used for a long time, and it is therefore necessary to change the position at which the carriers 34 are in mesh with the internal ring gear 38 or sun gear 36. Further, it is also necessary that the sun gear 36 and the internal ring gear 38 are moved up and down for the purpose of easily picking up the workpieces after their polishing process. In order to solve these problems, a lift mechanism for lifting the sun gear 36 and the internal ring gear 38 according to the prior art has a screw jack 46, which is attached to the internal ring gear 38 through an arm 48 while also attached to the sun gear 36 through the arm 48, coupling members 50, 52 and hollow driving shaft 40. When the screw jack 46 is operated, the internal ring gear 38 and the sun gear 36 are simultaneously moved up or down.
This lift mechanism for the sun gear 36 and the internal ring gear 38 becomes complicated in structure, thereby making its cost high. In addition, the sun gear 36 and the internal ring gear 38 cannot be moved up and down independently. Therefore, the position at which the carriers 34 are in mesh with one of gears 36 and 38 cannot be adjusted independently of the position at which the carriers 34 are in mesh with the other, although both gears 36 and 38 are differently worn by the carriers 34.